1. Field of the Invention
The present invention relates to an electron emission device, and in particular, to an electron emission device which has first and second substrates sealed with respect to each other and forming a vacuum structure.
2. Description of Related Art
Generally, electron emission devices are classified into a first type wherein a hot cathode is used as an electron emission source, and a second type wherein a cold cathode is used as the electron emission source.
The second type of electron emission device includes a field emitter array (FEA) type, a surface-conduction emission (SCE) type, a metal-insulator-metal (MIM) type, and a metal-insulator-semiconductor (MIS) type.
The MIM type and the MIS type electron emission devices have metal/insulator/metal (MIM) electron emission regions and metal/insulator/semiconductor (MIS) electron emission regions, respectively. When voltages are applied to the two metallic layers or to the metallic and the semiconductor layers, electrons are expelled and accelerated from the metallic layer or the semiconductor layer having a high electric potential to the metallic layer having a low electric potential, thereby creating the electron emission.
The SCE type electron emission device includes first and second electrodes formed on a substrate and facing each other, and a conductive thin film disposed between the first and second electrodes. Micro-cracks are formed in the conductive thin film so as to create electron emission regions. When voltages are applied to the electrodes while an electric current flows to the surface of the conductive thin film, electrons are emitted from the electron emission regions.
The FEA type electron emission device is based on the principle that, when a material having a low work function or a high aspect ratio is used as an electron emission source, electrons are easily emitted from the electron emission source when an electric field is applied thereto under vacuum atmosphere conditions. A carbonaceous material, such as carbon nanotube, or a sharp-pointed tip structure based on molybdenum Mo or silicon Si, has been developed for use as the electron emission source.
Although the specific structure of the electron emission device is differentiated depending upon the type thereof, the basic structure includes a first substrate, a second substrate facing the first substrate, and a sidewall surrounding the peripheries of the two substrates so as to form an inner space. The inner space is maintained in a vacuum state so that electrons are freely emitted and migrated therein.
Driving electrodes are formed on the first substrate to control the electron emission of the electron emission regions, and an anode electrode is formed on the second substrate together with phosphor layers so as to accelerate the electrons emitted from the first substrate toward the phosphor layers. With this structure, the phosphor layers are excited by the electrons emitted from the electron emission regions so as to emit visible rays, thereby causing light emission or image display.
The first substrate is commonly formed with glass so that it has a surface roughness which is altered in various manners. When, during preparation of the first substrate, structural components such as driving electrodes, insulating layers for insulating the driving electrodes from each other, and electron emission regions are formed, the surface roughness of the first substrate capable of optimizing the formation of those structural components has been left out of consideration.
When an insulating layer is formed on a first substrate with a high surface roughness, the surface roughness thereof is increased so that thermal distortion of the first substrate and the insulating layer is caused during the process of firing the insulating layer, thereby deteriorating the surface evenness of the insulating layer. The deteriorated surface evenness of the insulating layer causes cracks so that leakage of current through the cracks or a short circuit between the driving electrodes may result.
In contrast, when a driving electrode is formed on a first substrate with a very low surface roughness, the surface evenness of the driving electrode is enhanced, but adhesion of the driving electrode to the first substrate is reduced so that the driving electrode may be easily released during the subsequent processing steps.